


they had lights inside their eyes

by orphan_account



Category: Undertale (Video Game)
Genre: Canonical Character Death, Family Feels, Gen, Other, Platonic Soulmates, Soulmate-Identifying Marks
Language: English
Status: In-Progress
Published: 2016-02-23
Updated: 2016-03-01
Packaged: 2018-05-22 13:00:57
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,919
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6080358
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>you can bring the fire, i can bring the bones. </p><p>sans has four sets of words on his body.</p>
            </blockquote>





	1. before

**Author's Note:**

> so,,,i've wanted to write some kinda soulmate au for a while now, and one of my favs is the whole 'first words you hear them say are written somewhere on your body' thing, and i also love the idea of more than one soulmate???
> 
> and they don't necessarily have to be romantic, y'know? so most of the relationships here are platonic af
> 
> (also i like most gaster theories out there and i didnt wanna have to decide on anything so it's p vague)

 

 

sans has four sets of words on his body. 

which is odd, to say the least. most people only have one or two. one or two sets of words; one or two ‘soulmates’. four sets of words; four ‘soulmates.’

he, for one, isn’t sure how he feels about this concept of ‘soulmates’. this idea that out of everyone in the world, out of every monster (or human, maybe, but how unfortunate would that be), there is only one person (or two, or four??) ‘meant’ for you. only one other person that will make you feel whole. 

every monster is born with a soul. it is their primary source of life, of existence. every monster is born with a metaphorical hole in that soul, a little part of them that needs to be filled. with the presence of an alleged soulmate. (what, sans wonders, is the point of having a soul if there is something missing? what if you never find that missing piece? why does there have to be a missing piece in the first place?)

sans thinks that’s a pretty stupid name too— soulmate. the mating of souls. souls are just souls. he doesn’t get it. 

he doesn’t get it, and he doesn’t understand why he has _four_ little sentences marking his bones. what kind of monster is so empty that he needs four other souls to make him whole?

he doesn’t need anyone to make him ‘whole’, he insists with that self-assured confidence only small children possess. he’s perfectly fine by himself. 

(he spends a lot of time running his hands over the various letters when no one is around. he doesn’t like anyone looking at them. _he_ doesn’t like looking at them, but he does it anyway. such is his struggle.)

he doesn’t need anyone to make him whole, and when he is five years old he’s sitting in the waiting room of the hospital in Hotland, anxiously fidgeting with his hands in his lap. his legs aren’t long enough to reach the floor yet, so he swings them back and forth until they settle into a kind of rhythm. 

it’s a pretty busy place, this hospital. or at least, it usually is. but right now, it’s pretty early in the morning— he’d woken up to his dad shaking his arms gently with a strange kind of his urgency in his eyes, and then they’d all hurried to this little hospital, sans half awake and pretty confused. 

the air in this little hospital is different from the air outside, and he shivers. he wishes he remembered to bring his jacket. 

he also kinda wishes he was back at home- he’s still really tired, and no one had bothered to give him a real explanation of why exactly he’s here. mom and dad had disappeared in a flurry of panicky voices and fluffy nurses and a brief peck on his skull and a ‘wait here, sans. we’ll be out in no time, buddy’. he isn’t the best at telling time yet, but there’s a clock on the wall and he’s pretty sure ‘no time’ was a long time ago. 

the part of him that isn’t half asleep and vaguely annoyed with this whole thing is actually starting to get worried. he’s only been here like once before, and that was during the day, and the usual people who work here and always walk around aren’t here right now, so he has no one to ask what’s going on. 

he shuts his eyes tight and tries to focus on something else. the clock ticking in the background. count the seconds. it’ll help calm down, maybe. get his mind off of his worry. seconds turn into minutes, minutes he slowly loses count of, and just as he’s about to drift back to sleep, a door opens. 

he sits up quickly, rubbing at his eyes, and there’s one of the fluffy nurse ladies from earlier standing in front of him.

“Sans?” she asks. her voice is high and sweet. 

he nods. 

she smiles, “Please come with me.”

that sounds kind of ominous, but he slides off the chair and follows her anyways. his heart lifts when he’s led into a room and sees mom laying out on a bed and dad sitting next to her. there’s a little bundle in her arms. 

he runs forwards and jumps into his dad’s lap, who pulls him close and smiles tiredly. his mom looks exhausted, but she smiles too. he smiles back, because they both look so happy. then he zeros in on the mysterious bundle. 

why is she holding it like that? it just looks like a wrapped up blanket. did they come all the way to the hospital for a wrapped up blanket? 

they say a few things, but he’s too focused on the bundle, until, “Sans? Do you want to hold your little brother?”

he blinks. little brother?

“Uh- yeah, sure?” he asks more than answers. his mother carefully hands the blanket-bundle-thing to his father, who hands it to him just as carefully.

“Like this,” he says, holding the bundle to his chest in demonstration. 

sans holds the bundle to his chest- extra carefully, because this bundle seems pretty delicate- and looks down. peeking out of the blanket bundle, all wrapped up, is the sleeping face of the tiniest skeleton sans has ever seen.

he’s… startled? caught a little off guard? because this thing is _tiny,_ it’s so small, if he accidentally dropped the bundle… sans holds it a little tighter. the movement accidentally jostles the poor little guy, and sans freezes as the bundle shifts.

the tiny little skeleton blinks awake, much to sans’ awe, and seems to look around for a moment before his eyes lock on sans. his breath catches. he has no idea what to do, and finds himself waiting in anticipation. 

a few seconds pass, before the baby skeleton seems to smile, and makes a small sort of ‘nyeh’ sound and sans feels something in his soul light up— in more ways than one, because it’s _there,_ fourth rib down on the left, that little sound that never made any sense before because it wasn’t even a word?? and who would say that?? engraved in a strange sort of font and had bothered him for so long, one of the meaningless sets of words on his body that finally, suddenly has a meaning. 

“…wow,” he whispers, and this little baby skeleton- this little baby brother- makes that little sound again, and he laughs in amazement. 

“His name’s Papyrus,” he hears his mother say somewhere far away, and he smiles because of course that’s his name, only his little brother would have a name as cool as that. 

“Papyrus,” he repeats quietly. Papyrus smiles again, and he feels his dad’s hand on his shoulder, and this is easily one of the best days of his five year old life. 

(later, when they get home, they find that word- _‘wow’_ \- in the same place sans has his, only opposite- four ribs down on the right, in it’s own strange sort of font. 

and he’s overjoyed— ecstatic— and maybe, sans thinks, these words aren’t all that bad after all.) 

(he had always thought, throughout his five years of experience in the world, that soulmates were an inherently romantic thing?? but. but that wasn’t true. it was just about… feeling whole. who cared about those other three people? he had everything he needed right here.)

one down, three to go. maybe. 

 

sans has four sets of words on his body.

papyrus has three. one of them is sans’, just like one of sans’ is his. 

papyrus has three, and one day a few years later he comes running home with this excited little glint in his eye, dragging a little girl with dark red hair behind him. 

‘undyne’ is her name. papyrus had met her in Waterfall, apparently, and her first words to him had been ‘ _What kinda flower are you supposed to be?_ ’ because he had been sitting with the flowers, probably, like he enjoyed doing sometimes. 

and then sans understands that excited little glint, because papyrus has a question about flowers engraved on his left wrist, and sans is pretty sure this undyne girl has the answer to that question on her own. 

( _‘I’m not a flower, I’m a skeleton!’_ in papyrus’ unique font, clashing nicely with her scales, that she reluctantly shows with a stream of mumbles and a flushed face, and a ‘There’s no way I’m soulmates with a punk like you! You gotta get way stronger before we can make this official!’

sans doesn’t point out how it’s kinda already official, it’s been official since before they met each other, because it’s a lot more fun to see his little brother get all hyped about it— _a new friend, finally! and not only that, but my second soulmate! what an amazing day! i’ll get super strong, just you wait!)_

this undyne girl is kind of loud sometimes, and likes throwing things, but also doesn’t let papyrus do anything too dangerous and calls him a punk in an affectionate sort of way instead of insultingly, and they have sleepovers and practice their magic and shareDreams of The Royal Guard, and she’s pretty nice to sans, too, even if she calls him ‘Papyrus’ Brother’ a lot and says he should practice his magic more. 

‘i’m the older brother,’ he says as an excuse, but he’s not really sure how old undyne is, so maybe she’s the oldest?? he thinks she might be. he never asks her, because if she is then he might have to listen to her and he likes his title of ‘older brother’ a little too much for that.

this undyne girl is papyrus’ second. two down, one to go. 

sans doesn’t know if he wants to meet any more of his own.

 

undyne also has three sets of words. 

she tells papyrus this, who tells sans this, who is kinda surprised, because he thought one to two was the norm. though he’s never met anyone else with four.

undyne has three, and one day she’s busting through their door (they live alone now, in their own house) and yelling that ‘ _King Fluffybuns_ ’ is one of her soulmates!!!! (and he’s— where has he heard that nickname before? not from her, definitely not from her- from someone else, then?)

and then papyrus is yelling with her and she’s telling her story: how she went to attack the _king_ (???) and how she couldn’t do it, and how King Asgore actually seemed proud??? impressed??? and how his first words to her were _‘I apologize if I have done something to upset you, small one._ ’ and how those were the words written on her hip!!! and how he invited her to _train_ with him??? and how she was _definitely going to!!!_

it’s a pretty entertaining story, and papyrus is amazed, but sans is still caught up in the nickname part, because… he knows he’s heard that nickname before, and he knows it wasn’t from undyne.

she’s talking about how she has one more person left to find, how papyrus does too, and then she asks how many sans has left— _actually, how many do you have in the first place? i don't think i’ve ever asked._

‘Sans has three,’ papyrus answers for him, without skipping a beat. 

sans blinks. 

sans has four. he’s spent hours staring at all the different letters, all the different words in all their different fonts, so he _knows_ he has four. their conversation continues without him and he is left very confused. 

he is very confused, and feels almost suffocated in this little house of theirs— all theirs, and theirs alone, just the two of them, no parents, never knew their parents…?? their parents, at the hospital, the first time he held papyrus??? 

his head hurts.

he excuses himself, stumbles up the stairs to his room because he really does feel like he’s suffocating now, and he can’t be in that crowded room anymore, not when they never knew their parents?? and undyne calls asgore ‘king fluffybuns’?? and he has four sets of words?? he has four, so why did papyrus say three?

he shrugs his jacket off and lifts his shirt up to see the small ‘ _nyeh’_ papyrus marked him with. the only soulmate he’s met so far, when his brother and his friend have both met two. 

another one, disjointed letters running across three of his ribs on the right.

another one, a simple phrase along his collarbone. 

another one, a few small symbols on his radius— he chokes on nothing. the headache gets stronger. he doesn’t know why. 

he’s never seen those symbols before, but he has, he’s looked at them his whole life—

they don’t make sense, but they do— _‘you’re shorter than i expected,’_ — and he knows he’s heard it before, just like that time in the hospital. he’s heard it. 

(he’s heard it, and they live alone, but they didn’t always, because— because something happened to their parents? they had to work, he applied, he was turned away, he applied, he was accepted for something he never thought he’d be accepted for because he didn’t have the right experience and ‘ _you’re shorter than i expected’_ and white white coats and rare smiles and offers to move in and something really really bad and ‘don’t forget’ but he forgot, he forgot, he doesn’t know, he doesn’t know. 

he’s heard it and he has four sets of words but papyrus thinks he has three and he forgot and no one— no one remembers?? no one remembers. 

hell, he doesn’t even _know_ what no one remembers, snapshots and snippets that are too diluted to look at, these symbols on his arm that are too much to look at, they make his head hurt, ring, pound.

he doesn’t know. he doesn’t know. 

he knows they haven’t always lived alone, and he knows that he’s forgotten something important. but… but he doesn’t know.)

 

sans might as well have three sets of words on his body. 

 

 


	2. somewhere in the middle

**Summary for the Chapter:**

> and he… he hates making promises, he really does, but this mystery lady is nice, and likes his puns, and sounds like she might cry, and might maybe be his soulmate, so he says yes.

 

one day, sans is walking in the woods. 

the woods are a nice quiet place he visits a lot, because while he loves spending time at grillby’s, that nice restaurant he’s been frequenting ever since they settled in snowdin a while ago, he still needs some time to himself. 

his boundless charm may come naturally, but his amazing jokes need to be restocked every once in a while. 

his hands are buried in his pockets so he doesn’t have to look at his wrist— he hardly looks at his wrist. he has a big comfy jacket with long long sleeves that cover up his wrist. his hands are in his pockets so much he doesn’t have to bother even thinking about them. 

his hands are buried in his pockets and he hums a little tune while he walks and thinks, and by the time he stops humming and thinking, he realizes he’s never been this far into the woods before. it has a sort of ominous feeling— the trees are growing further apart, and the snow is getting a bit deeper. 

but it’s only mid-afternoon, and he won’t have to be back for a bit (he should be getting groceries right now, but what pap doesn’t know wont hurt him), and he hasn’t done anything very interesting for a while, not in this little town. so he shrugs his shoulders and decides to keep on walking. 

he keeps walking, and he keeps thinking, and he tries to come up with some nice cooking-related puns, because papyrus has started cooking (training?) more and more lately (and sans knows he enjoys the puns, even if he acts like he doesn’t sometimes).

he’s gotten two or three down before he looks up and abruptly comes to a stop, because: there’s a door. out in the middle (or maybe the end, now) of the woods. a pretty big door, now that he’s looking at it, big and grey and old looking— ruined looking. this is probably the entrance to the Ruins he’s heard about, then. 

and a huge door? of course his first thought is hey, what a great place to practice knock knock jokes. a huge important door for huge important jokes. 

so he grins, and walks up, and knocks on the door. no one answers, though he wasn’t expecting anyone to, so he answers himself, with a ‘who’s there?’ and he tells himself his joke and then he laughs about it, because it was a pretty good one. 

he wonders if maybe he’s one of his own soulmates, because those words are there too— _who’s there,_ in a nice swirly kind of font. not the same font papyrus has on his rib, so realistically it’s probably not him. how funny would that be though— a monster so lonely he has to be his own soulmate. or maybe narcissistic enough, but he’s never been too narcissistic. 

he keeps telling his jokes to no one, and no one answers. he tells his jokes to himself and he keeps answering and laughing until he’s satisfied with his new repertoire, and he walks back through the woods and decides that that door is his new favorite joke-practicing spot. 

so he comes back a few times, when he finds the time or when he’s bored enough, and he tells jokes to no one, until one day, he has a joke book in his hands and he’s sitting with his back to the door and he raps twice with his knuckles and says ‘knock knock.’

and the door replies, ‘who’s there?’

sans nearly jumps a foot in the air and then acts like he didn’t— he’s just a little startled, the door just _spoke_ to him— and then does what any reasonable person would do. 

‘dishes.’ he answers.

‘dishes who?’ the door replies.

‘dishes a very bad joke.’ 

there’s a moment of silence, before the door snorts, and then _laughs_ , and laughs and keeps laughing like it’s the best joke it’s heard in years. the door has a pretty nice laugh, a pretty feminine sounding one, and he realizes it’s probably not the door who’s talking.

there’s a lady inside of the ruins for some reason that really likes his joke and spoke the words written on his collarbone. _who’s there,_ in that nice swirly font. there’s that weird soul lifty feeling again, and he wonders if this mystery lady is feeling it too. 

the mystery lady responds with her own amazing joke, and that feeling grows, and he tells her another one and she tells him another one, and they keep telling each other these horrible (fantastic) jokes, and this is the most fun he’s had in a long time. 

eventually, he has to go, and she asks tentatively if he’d maybe like to come back tomorrow, because she has many more jokes to share that she hasn’t told him yet.

yeah, he says, sure, sounds good. 

(he doesn’t tell papyrus about the lady or the door, and he’s not really sure why. it just seems…personal, in some weird way. he doesn’t know, it’s whatever, he’ll tell him when the opportunity comes up.)

so he goes back the next day, and shares some more jokes, and laughs a lot, and he likes it a lot. 

he comes back the next day after that, and a few days after that, and at least once a week, because a secret pun buddy is something he’s never had before, and it’s kind of exciting. he thinks she might be the ‘who’s there’, but he’s not gonna ask. he’s not gonna ask because that’s kinda rude, and he’s not gonna be rude to this nice lady. 

he’ll enjoy her company instead, and tell her jokes, and listen to her jokes, and he thinks if she enjoys bad jokes this much she can’t be all that bad, and he vaguely hopes that maybe this lady has a ‘knock knock’ on her collarbone to match the ‘who’s there,’ on his.

 

undyne hangs around papyrus a lot, and papyrus hangs around undyne. 

it’s an… odd kind of dynamic, ‘i’ll suplex this boulder just because i can’ undyne and ‘would never willingly hurt a fly, ever’ papyrus, but it works.

undyne has three sets of words, and then one day she’s busting through their door again with enough force to nearly blow it off its hinges, yelling (again) about how she _met_ them, how she met her last soulmate _holy shit_ she met her she’s freaking out and sans has never seen undyne this flustered before?? 

it’s pretty weird.

papyrus wants to know _who_ this person is and _how_ they managed to make her like this, and she throws herself on the couch and gets up again and paces around and seems a little overwhelmed, so sans pats papyrus and whispers something about undyne maybe needing water because- y’know, being that flustered may not be too healthy for a monster that can barely stand to be in Hotland for more than an hour or two. 

she shoots him what might be a thankful look, but could also be confusion or annoyance— he isn’t sure with the way she’s moving so fast. pap rushes in with a glass of water that she gulps down violently (??) before jumping back onto the couch. 

then, she tells her new story: how king fluffybuns (sans scratches at his wrist) had sent her to do some business in Hotland (her least favorite place in the underground) to collect some papers from the royal scientist and deliver them back to him, how she’d never actually been inside the lab before and how the royal scientist answered the door and wasn’t anything undyne expected, how the first words the scientist said were, _‘o-oh, um, sorry, i wasn’t expecting you so soon,’_ (and she even did a little voice along with it) and yep, those were the words on her shoulder— complete with the little stutter.

and then she goes on to talk about how _short_ she is?? and how messy her workspace is?? and how she stutters a lot when she talks and how nervous she seems and how smart she is!!! how undyne could barely understand some of the stuff she was talking about when she gave her the papers!! and how amazing that was! and how she flushed when undyne told her that!! and how when she becomes captain of the guard soon, she’ll be seeing her a lot more!!

and he knows who it is from the minute she says ‘royal scientist’, but hearing her say the name- alphys!! isn’t that a sweet name!!- solidifies it. and honestly, he’s not all that surprised. 

he thinks they used to be buddies— more of buddies than they are now, which is to say sometimes they text each other bad memes or watch bad movies and throw popcorn at the screen because hey, sad friends gotta stick together, right? and they can talk about ‘that science stuff’ together, as pap calls it— back before something happened to whoever left those marks on his wrist, and he knows that undyne is totally someone she would fall for. 

papyrus asks (yells/asks?) if undyne told her, if they hugged or something, and undyne responds with a frustrated groan and a ‘no! i wussed out! i didn’t wanna scare her off or something- and what if she doesn’t have my words? what if it’s some sort of unrequited crap!? what if—‘

‘hey now,’ sans cuts in, because loud intimidating undyne doubting herself is not something he’s liking, surprisingly, ‘if i know alphys- and i do- she definitely has your words. i bet she was just too nervous to tell you.’

really?? undyne asks at the same time papyrus asks if he really knows her. yea, he says to both, trust me on this. 

…fine, she says, sounding suspicious but also relieved, and then asks how she should tell her. and that’s when papyrus cuts in, because he has like three dating manuals they’ve dug up at the dump and he’s an Expert on these things.

they spend the rest of the afternoon going over how to Flirt, how to Date, all the steps involved there, what she should say and how she should act until undyne snaps and chucks the books across the room.

and then picks them up and opens them again because she’s serious about this and she wants to do it Right. 

it’s kinda sweet, sans thinks absently from his place spread out on the couch. they’ll be good for each other. as he falls asleep to the sound of undyne practicing love confessions, he wonders if maybe he should go talk to alphys. 

(he does, eventually, and he’s right: she has undyne’s words on her shoulder— _‘you’re the royal scientist, right?’_ but she wasn’t sure it was undyne because really, anyone could say that, and there’s no way a ‘hot buff fish knight’ would ever be _her_ soulmate.

but she is, he tries to tell her, i’ve seen the proof, she wants to tell ya but she’s afraid to. 

alphys is afraid to tell her too, keeps insisting that there’s _no way_ , and even when she sort of maybe comes to terms with the possibility, there’s no way she’s gonna _tell_ her. not just gonna ask hey, do you happen to have a stutter on your shoulder?

it’s all kinda frustrating, the way they keep dancing around each other, but at the same time he guesses he understands, and no one will force either of them. 

still, it’d be a lot easier for everyone involved if they’d just fess up and kiss already.)

 

time passes.

undyne becomes captain of the royal guard

papyrus becomes a sentry— and, by default, so does sans.

he and the mystery lady keep trading jokes.

things are fine. 

but one day, the mystery lady doesn’t seem like she’s doing too hot. her laughs are weak and half-hearted, and her joke stutters and falls. 

‘what’s wrong?’ he asks, carefully, because they’ve never talked too deeply about stuff other than jokes and the occasional thing he has to say about papyrus.

she’s hesitant, and sorta quiet, so it’s kind of hard to hear through the door, but eventually she says, ‘if a human ever leaves the ruins… will you protect them for me? please? _please_ protect them, everything beyond the ruins is so dangerous, please.’

and he… he hates making promises, he really does, but this mystery lady is nice, and likes his puns, and sounds like she might cry, and might maybe be his soulmate, so he says yes. 

he says yes. he makes a promise he already sort of regrets. 

but the mystery lady sounds so relieved, so grateful, that he can’t really feel bad about it. 

(maybe he feels sort of bad about not telling papyrus, but papyrus is really set on capturing a human all of the sudden, and the opportunity has never really come up before anyways. how do you tell someone you’ve been trading jokes with a lady you’ve never seen before, you don’t know the name of, made a dangerous promise to, and might be your soulmate? you don’t, that’s how. she’s not doing anyone any harm, and neither is he.

a big part of him hopes a human won’t fall down for a really really long time.)

 

sans has four sets of words. three, sort of. 

pap has three and so does undyne and he’s not sure about alphys. most of his buddies around town have already found their soulmates (though it’s not very polite to outright ask how many someone has or if they’ve found anyone yet). he’s not sure about grillby though.

he and grillby, they go way back. sans has been frequenting his restaurant since they first moved to snowdin, and he had people recommending it to him back in New Home too. he’s a pretty nice dude. he lets him stay late sometimes and lets him ramble sometimes.

sans knows his wife died, and knows he keeps those words safely covered under his bowtie. grillby knows vaguely about sans’ parents and about papyrus and about those four sentences on his body. 

grillby’s a pretty nice dude, and a pretty good friend, and the first time sans climbed into a chair at the bar, he’d said, ‘i’ve heard you make the best burgers in the underground. how much for one of ‘em?’ and grillby had sort of paused, hand stilling where it was cleaning the rim of a glass, and looked at him oddly for a moment, before nodding and telling him the price.

it had been the _best_ burger he’d ever eaten. the deal had been sealed. this was his new favorite place. is still one of his favorite places, aside from the couch and maybe the door to the ruins. 

and grillby’s a pretty nice dude. a pretty good friend. grillby’s words aren’t there, aren’t on his collarbone or up a few of his ribs, but maybe a part of him wishes they were (and maybe if he tries hard enough he can convince himself that those weird symbols on his wrist are just what his crackling voice translates to, instead of something he doesn’t want to think about).

 

sans has four sets of words. he’s made a dangerous promise. 

and one day, a human walks out of the ruins. 

 

 

**Notes for the Chapter:**

> when ur sansby trash but didn't think abt it till the last minute and just decide to stick with what's closest to canon 
> 
> also i've been thinking about it a lot and realized i should prob tweak a bit with undyne but im too lazy to go back and rewrite lmao 
> 
> anyways, i want to expand on this so much more than i originally planned but ??? life's been p hectic, and im not sure if i have the motivation or time to do what i wanna do so ¯\\_(ツ)_/¯ but im always up to talking about it! if u wanna (or talk abt literally anything), hit me up at [snasy](http://snasy.tumblr.com/%20) on tumblr


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